Each year numerous people suffer a heart attack (acute myocardial infarction) due to the obstruction of a coronary artery which supplies blood to the heart muscle. Of this number, a significant percentage die before reaching medical attention. Another group succumbs after reaching the hospital. Of those which survive, more than half suffer permanent loss of a portion of the heart muscle owing to the damage done during the period of a heart attack by the lack of blood supply (ischemia). This damage impairs the quality of life, shortens life expectancy, and increases the probability of death with subsequent heart attacks.
Currently the methods of treatment of heart attack victims include:
(1) observation and medication in a coronary care unit;
(2) thrombolysis - dissolving by drugs the clot which blocks the coronary artery;
(3) percutaneous coronary angioplasty (PTCA) reopening the obstructed artery with a balloon dilator threaded through the arterial system;
(4) emergency operations for coronary artery bypassdetouring blood around the blockage with a blood vessel graft;
(5) balloon counterpulsation - relieving about 10-15 percent of the work of the heart with a pulsating balloon placed in the body's main artery, usually used as a temporizing measure prior to or during the foregoing methods of treatment; and
(6) assist devices - tubes temporarily left in the heart following a bypass operation where the heart is too weakened to support the circulation, even with the balloon treatment of (5) above.
Despite the best available therapy, a significant percent of the patient's die, and those who are not treated fairly promptly suffer permanent loss of heart muscle supplied by the blocked artery. The primary damage to the heart muscle during a heart attack occurs because of the blood supply to a portion of the heart being interrupted; and therefore, the primary goal of the treatments referred to above has been to restore the blood supply as quickly as possible. However, while some of the methods outlined above have decreased the time required to restore blood flow to the portion of the heart subjected to ischemia, they have not resulted in that heart muscle being able to restore its function to the degree previously hoped. Recent studies show that limitations of previous techniques of reperfusion to restore heart muscle function are due to their inability to control the conditions of reperfusion (for example, the blood pressure, the work of the heart) or the composition of the reperfusate blood. The solution used for this purpose keeps the region of the heart muscle from beating (cardioplegia) to minimize its need for oxygen. The cardioplegic solution contains oxygen because it is mixed with oxygenated blood from the heart/lung machine (blood cardioplegia).
Recent experimental studies have demonstrated that controlled reperfusion, which can be achieved via surgical intervention, may facilitate recovery of the left ventricular function after myocardial infarction to a greater degree than can be achieved using conventional pharmacologic or mechanical strategies. The September 1986 issue of the Journal of Thoracic and Cardiovascular Surgery, entitled "Studies of Controlled Reperfusion After Ischemia," discloses results of laboratory experience supporting the conclusion that controlled reperfusion is necessary. More specifically, it has been determined that damage can be avoided by administering a special blood cardioplegia reperfusate to the damaged area before normal blood flow is resumed. Tests on dogs and other animals indicate that the blood cardioplegia negates the adverse effects of toxins which build up in the myocardium during the ischemia caused by the obstruction of blood to that portion of the heart. The re-introduction of normal blood flow, without the cardioplegia, does not revive the oxygendeprived tissue and results in loss of all or a portion of the affected myocardium. It appears that the cardioplegia solution flushes the damaged capillary bed of toxins that have accumulated during the infarct episode. This cleansing apparently facilitates the recovery of the heart tissue when normal blood flow is resumed. Included in this issue is a preliminary series of patients treated by surgically controlled reperfusion who experienced the same excellent recovery of heart muscle function that occurred under experimental conditions. These results have been confirmed in a recent series of patients who were treated in a multi-center trial of thrombolytic treatment (TAMI) and who did not qualify for or failed the more conventional pharmacologic approach of thrombolysis. The surgical treatment was that of controlled reperfusion following the protocol described in the September 1986 Journal referenced above.
In addition, the studies referred to in the above-mentioned Journal have shown that the foregoing treatment produces good recovery only when the heart is decompressed (left ventricle vented) by extracorporeal circulation. Without such venting during the extracorporeal circulation, there can be sufficient blood returned into the ventricle to cause it to eject, and thereby raise the metabolic demands of the damaged muscle by stretching it.
The studies reported in the above-referenced Journal utilized open-chest techniques for the extracorporeal circulation, with a secondary pump for the venting of the ventricle to obtain the desired decompression condition. However, it is suggested that instead of an open-chest operation, a peripheral bypass technique be employed wherein catheters are connected to the vascular system. With a peripheral technique, catheters may be introduced percutaneously or by using a cutdown procedure along with vessel dilation.
The aforementioned Journal article (page 560) proposes an experimental model of a peripheral (in this case) femoral-to-femoral vented bypass system in humans, together with regional cardioplegia reperfusion, without thoracotomy. This, however, is a desired goal, and the specific manner and apparatus of accomplishing this is not disclosed in detail because it had not been done.
There have been some femoral-to-femoral bypass systems, such as in U.S. Pat. No. 4,540,399, but it is not clear that total bypass is obtained, and there is no provision for ventricular venting.
Summarizing some of the foregoing background, it can be simply stated that: heart attacks are caused by closed coronary arteries; opening an artery does not cure the heart attack; and controlling the conditions and composition of the initial reperfusion of a blocked coronary artery does permit salvage of the damaged myocardium beyond the obstruction. The only accepted way to control the conditions and composition of coronary reperfusion of individuals undergoing a heart attack is by open-chest surgical operation with direct decompression of the heart, decompression of the left ventricle and direct infusion of the coronary arteries through surgically connected saphenous vein grafts. Although the results of this approach have been proven superior to results obtained by any of the current methods of treating acute myocardial infarction, the performance of a major operation has risks of mortality and morbidity, and a high level of expense.
There is thus a clear need for an improved system which will minimize the damage to the myocardium following heart attacks. Such a system should be able to be applied quickly after the onset of symptoms. It should provide for the opening of the blocked artery without permitting normal blood flow to enter the ischemic area. It should permit infusion of a fluid of a specific composition under controlled conditions of temperature, pressure and flow. Further, the system should relieve the workload of the heart by supporting the body on an extracorporeal circulation to eliminate the flow work of the heart and relieve the left ventricle of all blood to eliminate pressure work of the heart. Further, it is highly desirable that the foregoing be accomplished without the risk of a major chest operation in critically ill patients.
It is also desirable that an improved extracorporeal circulation system be available for applications other than in connection with cardioplegia reperfusion.